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A transformation achieving the optimal symmetric N-->M cloning of coherent states is presented. Its implementation requires only a phase-insensitive linear amplifier and a network of beam splitters. An experimental demonstration of this continuous-variable cloner should therefore be in the scope of current technology. The link between optimal quantum… (More)
An analytical expression for the von Neumann entropy of the Laughlin wave function is obtained for any possible bipartition between the particles described by this wave function, for a filling fraction nu=1. Also, for a filling fraction nu=1/m, where m is an odd integer, an upper bound on this entropy is exhibited. These results yield a bound on the… (More)
The impossibility of perfectly copying ͑or cloning͒ an unknown quantum state is one of the basic rules governing the physics of quantum systems. The processes that perform the optimal approximate cloning have been found in many cases. These " quantum cloning machines " are important tools for studying a wide variety of tasks, e.g., state estimation and… (More)
We assess the security of a quantum key distribution protocol relying on the transmission of Gaussian-modulated coherent states and homodyne detection. This protocol is shown to be equivalent to an entanglement purification protocol using CSS codes followed by key extraction, and is thus secure against any eavesdropping strategy.
A study of the thermal properties of two-dimensional topological lattice models is presented. This work is relevant to assess the usefulness of these systems as a quantum memory. For our purposes, we use the topo-logical mutual information Itopo as a " topological order parameter ". For Abelian models, we show how Itopo depends on the thermal topological… (More)
A quantum cloning machine is introduced that yields M identical optimal clones from N replicas of a coherent state and N' replicas of its phase conjugate. It also optimally produces M' = M+N'-N phase-conjugate clones at no cost. For well chosen ratios N'/N, this machine is shown to provide better cloning fidelities than the standard (N+N')-->M cloner. The… (More)
exact-universal computation with qudits probability distribution of bi-partite randomised stabilizer states (6) 527 C.M. Dawson, The Solovay-Kitaev algorithm (1) 81 L. Deslauriers, see M. Acton S.J. Devitt, Robustness of Shor's algorithm (7) 616 E. D'Hondt, The computational power of the W and GHZ states (2) 173 T.G. Draper, A logarithmic-depth quantum… (More)
Publications dans des revues internationales avec commité de lecture: Classical Teleportation of a Quantum Bit N.